1) Field of the Invention
The present invention relates to a communication system for enabling a user to receive service from a service provider through a network. The present invention also relates to a communication method for enabling a user to receive service from a service provider through a network. The present invention further relates to a user terminal which can receive service from a service provider through a network.
2) Description of the Related Art
The development of economical, high-speed broadband network systems is rapidly proceeding so as to support widely spreading use of broadband multimedia services such as the Internet or digital contents delivery services. Actually, construction of network systems such as ADSL (Asymmetric Digital Subscriber Line) systems and FTTH (Fiber To The Home) systems are proceeding. In the ADSL systems, existing copper cables are utilized for realizing high-speed digital transmission. In the FTTH systems, optical fiber cables are laid to houses of users for providing high-capacity high-speed communication services to the users.
In addition, it is expected that as a result of the development of the network technologies, a number of service providers (xSPs) will become available and spur the expansion of the market of the network business, where the xSPs include internet service providers, contents service providers, and the like, and will provide high-quality image delivery services, music download services, and the like.
Further, recently, network services generally called virtual private networks (VPNs) have become available. The VPNs are private networks which are built over private local networks and public networks, and utilize services provided by public network providers as if the private networks are leased lines. For example, a private network can be virtually built by connecting local area networks (LANs) in a company through the Internet. When a private network is built in this manner, the private network becomes free from the physical network structure, and has high flexibility and expandability.
In the current circumstance, in which the broadband services are spreading as above, users' demands for flexible switching of a connection with each user between a plurality of service providers are increasing.
On the other hand, Ethernet (which is a registered trademark of the Xerox Corporation) is deemed to be a promising LAN technology for use in access channels and WAN lines. For example, efforts are moving ahead to standardize the 10 Gb/s Ethernet. A typical protocol for performing authentication and IP address assignment on the Ethernet is PPPoE (Point-to-Point Protocol over Ethernet). The authentication and the IP address assignment are necessary when a service provider to which each user is connected is switched.
FIG. 65 is a diagram illustrating a configuration for connecting a user terminal to service providers, where the service provider to which the user terminal is connected can be switched by using PPPoE.
A user terminal 100 can be connected to a service provider through an Ethernet, an ADSL or FTTH line, and an access network 600. The ADSL or FTTH line is terminated with a subscriber-side terminating device 110, which is an ADSL modem when the service is provided through ADSL, and an ONU (Optical Network Unit) when the service is provided through FTTH.
In order to establish a connection between the user terminal 100 and one of the service providers, the user terminal 100 initiates a call to the service provider and sends a user ID and a password to the service provider. When the user is authenticated, an IP address is issued to the user, and the service is started. When the user requests to switch the connection to the service provider, the user inputs the name of another service provider to which the connection is to be switched, following the user ID, and sends the user ID and the name of the service provider to which the connection is to be switched. Then, the access network recognizes the user's request, and switches the connection.
Since the above operations after the initiation of the call are performed in accordance with PPP (Point-to-Point Protocol), the IP address is delivered to the user by using IPCP (Internet Protocol Control Protocol).
PPP includes two layers: LCP (Link Control Protocol) and NCP (Network Control Protocol). LCP is used for establishment of a datalink which is independent of an upper protocol, and NCP is used for processing which is dependent on the upper protocol. In the case where the upper protocol is TCP/IP, IPCP is used as an NCP, and the IP address is determined in accordance with IPCP.
FIG. 66 is a diagram illustrating a conventional network system which uses PPPoE. The conventional network system of FIG. 66 corresponds to the configuration of FIG. 65. In FIG. 66, the terminating device 110 is not shown. The access network 600 includes switches 601 and a broadband remote access server (BRAS) 610. The B-RAS 610 is connected to servers respectively belonging to service providers.
In order to establish a connection between the user and a service provider, the user inputs “user-name@provider-name” into the user terminal 100, where the information “user-name” indicates the name of the user, and the information “provider-name” indicates the name of the service provider. Then, a packet including the information “user-name@provider-name” is sent to the B-RAS 610 through the switches 601. The B-RAS 610 transfers the packet to the service provider based on the information “user-name@provider-name”. Thus, the user can arbitrarily choose a service provider to which the user terminal is connected.
However, in the above conventional network system using PPPoE, processing concentrates in the B-RAS 610. Therefore, the processing load imposed on the B-RAS 610 becomes very heavy, and impedes high-speed communication The reasons for the concentration of processing in the B-RAS 610 are as follows.
(i) Since IP processing is required, it is necessary to assign an IP address to each interface connected to an xSP. In addition, an IP address is also assigned to each PPP virtual interface for point-to-point connection to the user terminal. Therefore, administration cost is increased. In this case, if sessions between the same user and the different xSPs are controlled by different B-RASs, the administration cost is further increased by necessity for statistical and accounting management.
(ii) Whichever xSP is connected to the user terminal 100, every frame from the user terminal 100 passes through the B-RAS 610, as illustrated in FIG. 66. According to PPPoE, user data such as IP packets, as well as management information for authentication and the like, are encapsulated for transfer in accordance with PPP. Therefore, the main signals to be transferred to the xSPs, as well as the management information, concentrate in the B-RAS 610.
(iii) In order to perform negotiation in accordance with PPPoE, it is necessary to exchange requests for conditions and acknowledgments (e.g., Configure-Request and Configure-Ack). Since the negotiated conditions differ with different users, the processing is executed by software.
(iv) In order to transfer information to the xSPs, the B-RAS 610 is required to perform layer-3 processing. That is, the B-RAS 610 has to perform the so-called virtual router function. In addition, the B-RAS 610 is required to handle a routing table for all interfaces, i.e., all of the provider-side interfaces corresponding to the xSPs and the PPP virtual interfaces corresponding to subscribers.
As described above, in the conventional network system using PPPoE, all of the various operations are performed by the B-RAS 610. Therefore, the B-RAS 610 becomes a bottleneck, which limits speedup of the conventional network system.